Ensuring safety in connection with use of equipment in certain areas is important. For example, equipment used in parts of a plant or work environment that are declared as explosion-protected areas should satisfy certain requirements that are laid down in safety standards. One example protection technique for operating equipment in an explosion-protected area is the so-called “intrinsic safety” technique. In this technique, the energy supplied to electrical equipment is limited such that no ignitable spark can be produced, even though the environment may contain an explosion-prone environment (combustible gas and oxygen). To limit energy produced by the device that may cause ignition of a combustion reaction/explosion, both current and voltage may need to be limited.
Intrinsically safe equipment is defined in safety standards (for example, ISA-60079-11 (12.02.01)-2009) to be equipment that can not release energy to cause ignition of a hazardous mixture in an easily ignited concentration. This may be accomplished by limiting the amount of power to be below a level that will ignite the gases. Moreover, each device that is “intrinsically safe” may be certified for differing levels of hazardous environments. Thus, a device should only be used in an environment matching its safety certification.
In a given environment a distinction may be made between different zones. For example, in certain zones, such as Zone 0 of the Intrinsic Safety Standard, a permanently explosive atmosphere is assumed. Other zones are described in the safety standards (Zone 1, Zone 2). Many jurisdictions (United States, Canada, European Union, et cetera) have adopted certification standards for devices to be used in such zones, thereby providing classification to the devices. In such an area where an explosive environment is presumed, there is exclusively permitted a resistive limitation of the current by one or more resistors which also satisfy certain safety requirements.
The functionality or availability of assemblies can also be increased considerably in an explosion-protected area when the assemblies are used redundantly or with multiple redundancy, wherein one assembly is active and further assemblies are on standby. Thus, if a fault occurs in an active assembly, a switchover to the further assemblies is effected automatically. The assemblies used may be active at the same time.
A device for the intrinsically safe redundant current-voltage supply for one or more electric loads in an explosion-protected area is known. This device includes at least two supply circuits for providing the current/voltage supply with a protection means for the intrinsically safe power limitation of the current supplied. As part of the protection means, the supply circuits each contain means for current regulation and/or limitation. Outside the explosion-protected area, a means for the resistive current limitation is connected in series to the supply circuits as further part of the protection means. The means for the resistive current limitation is arranged between the supply circuits and the explosion-protected area.